摘要:

AbstractIn the presence of an uncertain prior information about the value of the slope parameter, the estimation of the intercept parameter of a simple regression model with a multivariate Student‐t error distribution is investigated. The unrestricted, restricted and shrinkage preliminary test maximum likelihood estimators are defined. The expressions for the bias and the mean square error of the three estimators are provided and the relative efficiences are analyzed. A maximin criterion is established, and graphs are constructed for an arbitrary number of degrees of freedom (D.F.) as well as sample sizes. A criterion to select optimal significance level is also discusse

ISSN:0323-3847    

DOI:10.1002/bimj.4710390202

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

ISSN:0323-3847    

DOI:10.1002/bimj.4710390203

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractIn two recent papers, LÄUTER (1996) and LÄUTER, GLIMM, and KROPF (1996) have proposed a new class of exact tests for multivariate normal data with an inherent structure. These tests are based on the construction of scores that have a spherical distribution. The principle can be adapted to a variety of different situations, and it supports exact tests with small samples of high‐dimensional data.In this paper, an enhancement of that theory will be given regarding the problem of missing data. It provides a new mathematical understanding of mean imputation techniques, and it is also the basis for a modified principal component missing data algorithm described h

ISSN:0323-3847    

DOI:10.1002/bimj.4710390204

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractIn classical linear regression model for analysis of medical data concerning hepatic extraction of insulin and c‐peptide the fundamental assumption is that the subjects involved are of a similar nature. In reality, if this assumption is violated then the precision of the results is questionable. This paper suggests a robust alternative to overcome this problem. It is observed that the robustification may be a better option to determine an optimal quantity of insulin which minimizes the risk of damage associated with diabatic treatment

ISSN:0323-3847    

DOI:10.1002/bimj.4710390205

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractSuppose it is desired to determine whether there is an association between any pair ofprandom variables. A common approach is to testH0:R=I, whereRis the usual population correlation matrix. A closely related approach is to testH0:Rpb=I, whereRpbis the matrix of percentage bend correlations. In so far as type I errors are a concern, at a minimum any test ofH0should have a type I error probability close to the nominal level when all pairs of random variables are independent. Currently, the Gupta‐Rathie method is relatively successful at controlling the probability of a type I error when testingH0:R=I, but as illustrated in this paper, it can fail when sampling from nonnormal distributions. The main goal in this paper is to describe a new test ofH0:Rpb=Ithat continues to give reasonable control over the probability of a type I error in the situations where the Gupta‐Rathie method fails. Even under normality, the new method has advantages when the sample size is small relative top. Moreover, when there is dependence, but all correlations are equal to zero, the new method continues to give good control over the probability of a type I error while the Gupta‐Rathie method does not. The paper also reports simulation results on a bootstrap confidence interval for the percentage bend correl

ISSN:0323-3847    

DOI:10.1002/bimj.4710390206

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

ISSN:0323-3847    

DOI:10.1002/bimj.4710390207

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractCase‐cohort and nested case‐control sampling methods have recently been introduced as a means of reducing cost in large cohort studies. The asymptotic distribution theory results for relative rate estimation based on Cox type partial or pseudolikelihoods for case‐cohort and nested case‐control studies have been accounted for. However, many researchers use (stratified) frequency table methods for a first or primary summarization of the most important evidence on exposure‐disease or dose‐response relationships, i.e. the classical Mantel‐Haenszel analyses, trend tests and tests for heterogeneity of relative rates. These can be followed by exponential failure time regression methods on grouped or individual data to model relationships between several factors and response. In this paper we present the adaptations needed to use these methods with case‐cohort designs, illustrating their use with data from a recent case‐cohort study on the relationship between diet, life‐style and cancer. We assume a very general setup allowing piecewise constant failure rates, possible recurrent events per individual, independent censoring

ISSN:0323-3847    

DOI:10.1002/bimj.4710390208

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractOn the basis of the conditional distribution, given the marginal totals of non‐cases fixed for each of independent 2 × 2 tables under inverse sampling, this paper develops the conditional maximum likelihood (CMLE) estimator of the underlying common relative difference (RD) and its asymptotic conditional variance. This paper further provides for the RD an exact interval calculation procedure, of which the coverage probability is always larger than or equal to the desired confidence level and for investigating whether the underlying common RD equals any specified value an exact test procedure, of which Type I error is always less than or equal to the nominal α‐level. These exact interval estimation and exact hypothesis testing procedures are especially useful for the situation in which the number of index subjects in a study is small and the asymptotically approximate methods may not be appropriate for use. This paper also notes the condition under which the CMLE of RD uniquely exists and includes a simple example to illustrate use of these techn

ISSN:0323-3847    

DOI:10.1002/bimj.4710390209

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe paper deals with modelling of experiments carried out in incomplete split‐block designs. Moreover, the characterization of the design with respect to a general balance property is given. Also, some statistical properties of the design are examined. The problems considered are illustrated with example

ISSN:0323-3847    

DOI:10.1002/bimj.4710390210

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThis article is concerned with an approach to disconfounding effects in repeated measure designs with multiple groups. An extension of latent curve analysis (MEREDITH and TISAK, 1990; RAO, 1958, 1965) is described. The method permits estimation and testing of intervention effects separately from temporal effects. It is based on restricted factor analysis of individual change profiles and utilizes basis curves representing group patterns of change. The approach is illustrated on data from a two‐group intervention stud

ISSN:0323-3847    

DOI:10.1002/bimj.4710390211

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY